In a small pot reduce the 2 cups of apple cider vinegar to 1/3 of a cup. Before I put the vinegar in the pot I measure 1/3 cup of water and pour it in so I have an idea of how much a 1/3 cup looks like in the pot I used. Once the vinegar has reduced set it aside.
In a microwave safe container heat the heavy cream, butter and cinnamon until the butter has melted and the mixture is steamingt. Set aside until the sugar has been caramelized.
Prepare an 8x8-inch pan by lining it with two pieces of parchment paper to create a sling.
In a medium pot heat the sugar, corny syrup and water over medium heat, do not stir, once everything is liquid you can swirl it occasionally to even out the color. Cook the sugar until it is a dark amber color, don’t take it too far or it might taste burnt.
Remove from the heat and add the heavy cream mixture and vinegar, it will bubble and boil up so be prepared for there to be a lot of steam.
Cook the caramel mixture for about 10 minutes on medium low heat until a candy thermometer reads 250F.
Pour the caramel into the prepared pan and let cool for 5 minutes before sprinkling with salt if desired. Let cool about 2 hours and then cut into squares and wrap in clean parchment paper.